[osm2pgsql] Attempt to improve the transaction management during "going over pending ways/relations"

Using an extended transaction on the planet_osm_ways table during the pending ways phase should be fine.
It is the planet_osm_rels table that needs to stay out of transaction in this phase, as the different pending
ways processes can simultaniously update the pending status of the same relations if multiple ways occur in a relation

Remove the extended transactions in the going over pending relations phase on the output tables.
The processing of relations during diff-import causes the ways to be removed from the output tables.
If a way is contained in two relations in the same diff, that also happen to be processed in different
parallel processes, this could dead lock.